Investments - Summary of Owned Real Estate Activity (Footnote) (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Property
Dec. 31, 2018
USD ($)
Real Estate [Line Items]      
Revenue producing capitalized expenditures $ 10,000 $ 45,000  
Net investments 5,943,530 5,468,563  
Intangible lease liabilities, net (121,902) (127,335)  
Net balance 5,821,628    
Non-revenue producing capitalized maintenance expenditures 2,500 4,600  
Held-for-use      
Real Estate [Line Items]      
Gain on disposal of assets for properties 10,200 26,500 $ 1,400
Held-for-sale      
Real Estate [Line Items]      
Gain on disposal of assets for properties $ 14,200 32,400 $ 13,000
Deed-In-Lieu Properties      
Real Estate [Line Items]      
Amount of disposition of real estate   $ 800  
Number of properties disposed | Property   1